Slot antenna array useful with top mounted beacon light and decoupled internal powerline



May 23, 1967 zucco 3,321,762

SLOT ANTENNA ARRAY USEFUL WITH TOP MOUNTED BEACON LIGHT AND DECOUPLED INTERNAL POWER LINE Filed May 27, 1964 l I I -15 I. I5 i,

- I8 3/ I Fig. 2 1 i l I Q/IG I I4' v I i INVENTOR. (an 29 Bruno Zucconi Attorneys United States Patent 3,321,762 SLOT ANTENNA ARRAY USEFUL WITH TOP MOUNTED BEACON LIGHT AND DECOU- PLED INTERNAL POWER LINE Bruno Zucconi, 2814 19th St., San Francisco, Calif. 94110 Filed May 27, 1964, Ser. No. 370,405 8 Claims. (Cl. 343--721) This invention relates to antenna arrays and more particularly to slotted antenna arrays and apparatus for feeding such arrays.

As known in the art, a slot antenna generally comprises a slot which is formed in a conductive member. The shape of the slot may take a variety of :forms, although a simple and common slot is rectangular in shape and approximately a half wavelength long at the operating frequency. In general, electromagnetic energy is fed to opposite sides of the slot at its midpoint. According to Babinets principle, the radiation patterns of a slot and a dipole are identical except that the electric and magnetic field vectors are inter-changed. The electromagnetic radiation emanated from a dipole is generally regarded as due to an electric current flowing on the metal conductor, whereas the radiation from a slot is generally regarded as due to a magnetic current flowing in the aperture. As with the dipole antenna a number of slot antennas may be arranged into an array.

One especially convenient form of such array may be generated by cutting a series of elongated spaced slots longitudinally into the surface of a cylinder. If each of the slots is energized in phase they will, according to Babinets principle, tend to radiate electromagnetic energy in a pattern analogous to that of arranged series of dipoles. As is apparent, the feeding of the individual slots raises a problem especially when it is desired to keep the effective diameter of the antenna as small as possible.

Accordingly, it is an object of the present invention to provide an improved method and means of feeding electromagnetic energy to a slotted antenna array.

Another object of the present invention is to provide an antenna array which is adjustable so as to produce or minimize lobing effects in the radiated pattern.

Another object of the present invention is to provide an antenna configuration of the type described through which a conventional electric power line may be passed so that a warning light may be placed upon an end thereof Without generating unwanted 6O cycle electromagnetic fields in the antenna.

A further object of the present invention is to provide a slotted antenna array which is completely enclose and weatherproof.

Another object of the invention is to provide an antenna of the above mentioned character which is relatively simple in construction and inexpensive to manufacture.

Additional objects and features of the invention will appear from the following description in which the preferred embodiments are set forth in detail in conjunction with the accompanying drawings, of which:

FIGURE 1 is a longitudinal cross-section view of an antenna array constructed in accordance with the invention.

FIGURE 2 is an enlarged diagrammatic cross-section of the center portion of the antenna shown in FIGURE 1.

FIGURE 3 is a transverse cross-sectional view of the antenna taken from the section lines 33 as shown in FIGURE 1.

In general the invention includes an antenna array which is formed of an elongated conductive member in which are cut longitudinally aligned collinear slots. There is disposed within the tube a center fed parallel wire transmission line. The line is connected to each of the slots by a pair of conductive members.

More particularly, referring now to FIGURE 1, there is shown a preferred embodiment of my invention. The basic structural member of the antenna is a tube 11, which may be of any suitable conductive material, such as aluminum, having plurality of elongated cut out portions or slots 12. The tube 11, may be of any convenient cross-section as for example, square or cylindrical. It may be noted that a cylindrical tube possesses certain advantages such as low material and production costs. As shown, the slots 12 are cut into the wall of the cylinder in a generally collinear array, the length, width and facing of the slots being determined by the desired radiation pattern and by the frequency of operation as will be more fully discussed hereinafter.

Electromagnetic energy is fed to the slots by a transmission line formed of two tubular conductive members 13 and 14 which are disposed parallel to each other and symmetrically about the center axis of the tube 11. The tube 13 forms a :feed tube and tube 14, a distribution tube transmission line is center fed at the midpoint of the distribution tube 14 by a coaxial transmission line formed of a center conductor 16, an outer conductor formed by the feed line 13 and insulating material 17. Power is fed the coaxial transmission line to midpoint 15 of the distribution line. Center conductor 16 is connected to the distribution line by any suitable method such as by securing with a screw 18. Shoiting plates 19 are provided to give support to the distribution feed lines at their ends and also to provide a radio frequency and direct current short at the terminal ends of parallel transmission line. Distribution tube 14 may have disposed therein a suitable power line cord for the purpose of transmitting conventional alternating current power to a warning beacon 20 afiixed to the upper end of the antenna. The beacon 20 may include a bulb 21, socket 22 and protective cover 24 attached to an upper end cap 23 which may be screwed down over the end of the tube 11. Inasmuch as the power line to the beacon 20 runs entirely within the hollow portion of the distribution line 14 there will be no electromagnetic fields generated outside the tube 14 of the transmission line.

The lower end of the tube 11 may be provided with a suitable end cap 29. As a matter of convenience distribution tube 14 may have disposed thereupon a suitable fitting 28 adapted for being secured to a mast structure or mounting (not shown). Feed tube 13 may also serve as the outer conductor of the coaxial feed line and may be provided with a fitting 27 for mating with the transmitter transmission line.

As shown, dielectric plastic discs 31 and 41 support the parallel line transmission line at its midpoint and at the midpoint of each slot. The means of tapping the transmission line to feed the individual slots 12 is shown in FIGURE 3 and consists of two straps 32 welded respectively to each member of the transmision line and extending to a respective side of an adjoining slot. The contact between the straps and the side walls of the slots and the contact between the straps and the transmission line may be made by any suitable means such as, for example, by screws 33. There are, of course, one pair of straps for each slot of the antena. A strip of plastic forms a window 3-5, which covers the entire length of the tube over the area in which the slots are cut. The Window 35 may be secured to the tube by metal extrusions 37 which may be screwed or otherwise secured to the tube. This protects the interior of the tube from weather.

In operation the electromagnetic energy is fed to the slots through the elements in the following order: electromagnetic energy is delivered to the coaxial feed cable which transmits it to the transmission line at its midpoint. The energy is in turn transmitted through the straps to the midpoint of the longitudinal edges of each of the slots.

The dimensions of the antenna array are determined by the frequency of the radiation supplied to the array and by the number of radiating elements desired. In the figures there is shown an eight element array. Each slot of the array is made a length sufficient to cause reso nance and is approximately eight/ tenths of the free space characteristic wave length at the mid-frequency of the frequency band of operation. The slots are spaced approximately one wave length apart except that the center two slots are approximately one and one-half wave length apart. The slots are .much less than one wave length in width.

The center-to-center spacing of the two center slots of the array is made approximately one and one-half (1 /2) free space wave lengths in order to make the length of the transmission line from the closest slot of each array of four slots to the midpoint of the eight slot array equal to approximately three-fourths A) of a wave length.

This spacing takes advantage of the impedance transformation existing at odd multiples of quarter wave lengths along a transmission line. The center-to-center spacing of adjacent slots in each array is one free space wave length. Consequently, a substantially uniform amplitude and phase distribution along the entire array is achieved. The parallel tube transmission line is terminated in a short one-quarter A) wave length beyond the feed point of the last shot at each end of the array. This short is established by a conductive bar which places the ends of the transmission line at a DC. and RF ground potential. One or more spacers 31, made of a high dielectric, low loss material, are placed on the three-quarters wave length sections of the transmission line between the central feed point and the feed point of the first slot of each array, causing impedance discontinuities along this section of the transmission line. By varying the position of these impedance discontinuities the overall impedance transformation along this section of the line may be varied thus giving control over the terminal or feed point impedance of the array. It is essential that the position of these impedance discontinuities be maintained symmetrical with respect to the central feed point of the array so that lobing of the radiation pattern of the array in vertical plane does occur. Of course if lobing is desired, it may be obtained by a symmetrical positioning of the spacers.

If the tube 11 is made cylindrical it can be shown that the radius of the cylinder should be small compared to the characteristic wave length. When this condition exists, the radiation pattern will approach an omni directional pattern in the transverse plane to the longitudinal axis of the tube cylinder.

While the invention has been disclosed with respect to the preferred embodiment shown, it will be apparent to those skilled in the art that numerous variations and modifications may be made within the spirit and scope of the invention and thus it is not intended by the inclusion of a single preferred embodiment to limit the invention except as defined in the following claims.

I claim:

1. In an antenna array, a first tubular conductive memher, said member having a plurality of elongate slots therein, said slots being spaced along the length of said member, a parallel conductor transmission line disposed within said tubular member, one of the conductors of said transmission line comprising a second tubular member having an opening through its side, a conductor disposed within said second tubular member to form therewith a coaxial transmission line for feeding the parallel transmission line at a location intermediate its length, said conductor being passed through said opening and electrically connected to the other conductor of said parallel transmission line, and means for electrically connecting eacn of said slots to said parallel transmission line.

2. An antenna array as in claim 1 in which said opening is located at the midway position among said slots.

3. An antenna array as in claim 1 wherein said slots are one electrical wave length apart.

4. An antenna array according to claim 1 in which said other transmission line member is tubular and further including a power line disposed in said other transmission line member and a beacon disposed at one end of said antenna array, said beacon being connected to said power line.

5. An antenna array according to claim 1 in which said plurality said slots are collinearly arranged.

6. An antenna array according to claim 1 including shorting means for terminating said parallel transmission line in a short one-quarter wave length beyond the feed point beyond the last slot at farthest end of each array.

7. An antenna array according to claim 5 further incluing an elongate strip of plastic sheeting covering said slots and means for securing said plastic sheeting to the outside of said first conductive member in weathertight relationship over said slots.

8. An antenna array as in claim 1 in which the distance from each slot to the point at which the parallel transmission line is fed is an odd multiple of quarter wave lengths.

References Cited by the Examiner UNITED STATES PATENTS 2,658,143 11/1953 Fiet et al. 343-770 2,665,382 1/1954 Smith et al. 343-770 2,744,249 5/1956 Shively et al. 343-770 X 2,778,015 1/1957 Chu 343-770 ELI LIEBERMAN, Primary Examiner. 

1. IN AN ANTENNA ARRAY, A FIRST TUBULAR CONDUCTIVE MEMBER, SAID MEMBER HAVING A PLURALITY OF ELONGATE SLOTS THEREIN, SAID SLOTS BEING SPACED ALONG THE LENGTH OF SAID MEMBER, A PARALLEL CONDUCTOR TRANSMISSION LINE DISPOSED WITHIN SAID TUBULAR MEMBER, ONE OF THE CONDUCTORS OF SAID TRANSMISSION LINE COMPRISING A SECOND TUBULAR MEMBER HAVING AN OPENING THROUGH ITS SIDE, A CONDUCTOR DISPOSED WITHIN SAID SECOND TUBULAR MEMBER TO FORM THEREWITH A COAXIAL TRANSMISSION LINE FOR FEEDING THE PARALLEL TRANSMISSION LINE AT A LOCATION INTERMEDIATE ITS LENGTH, SAID CONDUCTOR BEING PASSED THROUGH SAID OPENING AND ELECTRICALLY CONNECTED TO THE OTHER CONDUCTOR OF SAID PARALLEL TRANS- 